The low speed tunnel L-1

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10 pr.1961

VLiEGTUIG:::OUWKUNDE

Hichiel de uyterweg 10 • DELFT

00 TRAINING CENTER FOR EXPERIMENT AL AERODYNAMICS

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TCEA TM 8

THE LOW SPEED TUNNEL L-1

b Y

P.E. COLIN

Rhode-Saint-Genèse, October 1960

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TCEA TM 8

INTRODU CT ION

The low-speed wind tunnel L-1 is the 1argest testing faci1ity at T .C.E.A. and, comp1eted in 1.950, it is the oldest still in existence at the Centre; the Eife1 tunnel built in 1923 was dismantled in 1958.

L-1 is a low-speed tunnel of unusua1 design in that it can be operated in three different configurations :

(1) as an open jet tunnel of 3 metre dia. (9.8 feet),

(2) as a c10sed working section tunnel of 2 metre dia.(6.5 feet) and (3) as a vertica1-jet (spin) tunnel of 3 metre dia •

. Changes in oonfiguration can be obtained easi1y by the movement by means of auxiliary e1ectric motors of certain parts of the circuit.

All three configurations have a common length of return circuit which inc1udes the two contrarotating fans driven by a D.C. motor whos.e continuous rating is 580 KW. The rotational speed of the fan is controlled by a Ward-Leonard system.

A six component mechanical balance of the suspended type can be used with either of the two horizontal working sections.

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TCEA TM 8 1

GENER~L LAYOUT

Fig. 1 shows a plan view of the tunnel with the closed working section in operation. When not in use this section with its diffuser (B) is stored alongside the return circuit as indicated by dotted lines. The position of the open jet section A when not in use is also shown. The displacement of both A and B sections is made electrically along rails fixed to the ground.

To obtain the third configuration, namely the vertical jet tunnel which operates with a mainly open return circuit, the fQurth corner and cont-raction cone Care rotated through 900 _{about the axis ss. Fig. 2 shows a view}

in elevation of the vertical-jet configuration. Above the working section, the air is deflected from the ceiling of the building by corner vanes and returns through the building to the intake I which is lowered in front of the entrance to the first corner, sections A and B being located in their stored position.

The driving system is shown on fig. 1 with the d.C. motor M, the two contra-rotating fans F with driving gears and bearings located inside a stream-lined nacelle and the lubricating system L instalied just outside the tunnel.

The part of the tunnel starting at the first corner and ending just af ter the third corner is made in reinforced concrete. The first three cas-cades of corner vanes are made in pre-stressed concrete. The contraction cone with the fourth corner is made of light alloy. Sectio~A and B for the open jet and closed working section configurations respectively are made of steel plates welded together. The diffusers in the circuit have total angles varying between 5° and 6°.

A honeycomb is located just ahead of the contraction cone as shown in figs 1 and 2. There are no turbulence sreens.

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2 TCEA TM 8

DRIVING SYSTEM

D.C. current is supp1ied to the driving motor by a motor-generator

set. The power rating for continuous operation is 580 KW but the motor can

be overloaded for a 1imited time of 15 minutes to 870 KW.

Speed control is achieved through the field current of the generator

by acting on the excitation of the auxi1iary field generator. Fig. 3 gives a

schematic 1ayout of the electrica1 circuits.

The drive shaft from the motor enters the tunnel at the second corner

and is directly coupled to the first stage of the fan system consisting of ten

magnesium a110y blades. The second stage of nine b1ades is driven at the same

speed but in the opposite direction through an inverter gear system. Bearings

and gears are housed in a streamlined nacelle. The ang1e of 'pitch of the

b1ades can be adjusted at rest.

The 1ubricating system 10cated outside the tunnel consists of an oi1

tank with heating elements for cold weather operation, an auxiliary oil pump

whi'ch is overridden at a given fan speed by a main oil pump geared in the

nace11e to the drive shaft~ and an oi1 cooler (using water) for hot weather

or high-power operation. Electrica1 thermometers are installed at all the

bearings of the drive system so that temperatures ean be checked during

oper-ation.

OPEN JET TUNNEL CHARACTERISTICS

The working section has a diameter of 3 m (9.8 feet) and is 4,60m

long (15 feet). In this configuration, the axis of section A (fig.1) is made

to coineide with the axis of the tunnel; section A consisting of a collector

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A 1 and a cy1indrical pipe A 2. The collector is of variabie geometry being

made of four equa1 longitudinal sections which are pivoted at the downstream

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TeE. TM S 3

iucreases the flare d~ameter and the size of the fourlongitudinal slots

separ-ating the sections thus increasing the leakage in the collector. The opening

of the flare is adjusted as to avoid pulsations of the air in the jet which

can be extremely violent. The setting adopted was determined during the

early calibrq.tion of the tunnel. A rather small flare opening has been chosen"

together with the additional leaks produced by 2 rows of 36 holes of O~2 m.

diameter drilled around the circumference of the cylindrical pipe A 2 just downstream of the collector A 1. Under .these conditions the tunnel is free

of pulsations and there are no measurable statie or dynamic pressure gradients along the working sectiQn from 1 meter (3 feet) to 4 meter (13 feet) down-stream of the contraction cone.

The maximum continuous speed of the tunnel is 65 m/sec and the

maxi-m~m variation of the dynamic pressure across the working seétion is +1% of the mean value.

The cpntraction ratio for this tunnel is 4.

A six component mechanical balance, which is described in some detail below, is supported on reinforced concrete beams above the working section,

A three-point suspension is used for the models. The two forward points are located 2 m (6.5 feet) downstream of the contraction cone.

THE CLOSED WORKING SECTION C~CTERISTrCS.

For this configuratipn, the axis of section B is made to coincide ~ith

the axis of the tunnel as in fig. 1.

The diameter of the working section is 2 m (6.5 feet) and its length 2.5 m (8 feet). Access is obtained through two large door fitted with plexi-glas windows. Section B begins with a small contraction to reduce to 2 m the exit diameter of the main contraction cone C.

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TCEA TH 8

The maximum velocity is UO m/sec (360 ft/sec) ~nd the maximu~

vari-a:tion of dynamie pres'sure is

±

1% across the working section •

The contraction ratio is 9.

The six component mech~niea1 ba1ance càn a1so be used with this tunne1~

THE VERTICAL JET TUNNEL CHA&\CTERISTICS

The conversion to the vertica1 jet tunnel is achieved by displ~cing

section A or B whichever is in operation, away from the center line of the

tunnel to its stored position, rotating the contraction cone C to its

verti-cal ,posi,tiop and lowering tQe intake fairing I in front of the first corner

section. These operations can be performed in fifteen minutes approximately

or lass if the fairing I is not used, Electric ~otors control the

displace-ment Qf the moving parts. Rotation of the contraction cone C which is balane· ed is done through a 2 H.P. motor in approximately 30 sec.

A photographic view of the working section is given in fig.4. The

jet diameter is 3 m (9.8 feet) and the maximum velocity 30 m/sec (100 ft/~ec).

The working section starts at the lower end of a slightly diffusing cylindri-calsection K of 2.1 m length which is lQwered 1.1 m into the contraction

cone C. Wire grids are attached to the ~ower end to produce a suitable

stabi-lizing saucer shaped velocity gradient across the working section for tests

on free spinning modeis. When in position,'section Kprotrudes 0.7 m into

the test room and is followed by the open jet part 1.75 m long of the work-ing section. The air is then collected into the cylindrical duet L attached

to the cascade of turning vanes located near the ceiling. There is a slight .

gradient in static pressure along the working section in order to stabilize the height of free-spinning modeis.

Equipment for thi~ tunnel includes a vacuum chamber for checking tha

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TCEA TM 8 5

triggering system for the control surfaces of models under test. This latter system uses d.c. current produced by a small auxiliary motor generator set available in the low-speed tunnel laboratory. The current when switched on energizes a 48 wire coil surrounding the working section, thus producing a magnetio field. This field acts on a small magnet located in the model being tested thus triggering the control surfaces which have been se1ected to oper-ate. The electrica1 circuit is shown on fig. 5. To operate the system, the "contactor" 1 having been switched on, button 2 is pressed so energizing coil 3 and closing switch 4 in the d.c. 1ine to the ma in coil around the working

section. Af ter 3 seconds the time de1ay switch 5 opens through the action of

coi1 6 of the delay switch. The system is thus ready again for operation.

THE SIX-COMPONENT MECHANICAL BALANCE

The balance is supported on two reinforced concrete beams above the center line c;>f the tunnel. The general lay-out is shown in fig.6. The model is supported in the inverted position at 3 points. The two forward points which fix the pitch axis are 0.8 mapart; the rear point can be adjusted by

2 cm steps from 0038 m to 0.56 m aft of the pitch axis. Except for the part

of lift taken by the wire attached to the rear suspension point the aerodyna-mic load on the model is transmitted through a strut or wire suspension system

to two box structures with 3 arms each which are attached to the lower plate

but can rotate about vertical axis passing through the front wspension points.

Linkages, which are shown in the photograph of fig.7, conneet the

lower plate to the balance e1ements fixed to the upper plate, and are such as

to separate the aerodynamic load on the model into the three components of

force and the three components of moment. The ranges for the 6 components

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6 TCEA TM 8 Component Range Lift kg -170 to + 600 Drag kg - 35 to + 125 Side Force kg - 60 to + 60 Pitching moment k~ - 26 to +

44

Rolling moment k~ - 28 to + 28 Yawing moment k~ - 28 to + 28

The angles of incidence and yaw of the model can be changed during tests. Their ranges are

±

300 _{for incidence and for yaw.} _{Pitching movement}

is obtained by raising or lowering the wire attached to the rear suspension point. Yaw control is achieved by rotating the whole balance through the desired anglej the 3 armed box structures rotating automatically through the same angle in the opposite direction to keep the struts or the profiled sus-pension wires aligned to the air flow. The six balance elements are all the same, their range being 70 kg. They are auto-balancng, the equilibrium sen-sing device being a hydraulic one. The displacement of the rider weight on the screw beam is controlled by an oil servo motor, the number ofwrns of the screw beam to restore equilibrium being proportional to the disturbing force applied to the balance element. All readings are transmitted by selsyn.systems to counters installed in the control room near the tunnel. Forces are given directly in kg and moments in k~. Changes of incidence and yaw are also operated from a desk in the control room.

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TCEA TM 8 7

HIGH-PRESSURE AIR SUPPLY

High-pressure air is avai1ab1e in the L-1 tunnel for tests requiring high energy air such as in boundary-1ayer control. The system (see fig.8) inc1udes a 10 m3 reservoir (350 Cu ft) in which air can be stored at 15 atmos-pheres absolute, a 10 H.P. two stage reciprocating compressor, a 4 ins.

air duct, two pressure regulating valves set in parallel to keep downstream pressure constant at the desired va1ue, and an orifice p1ate for mass flow measurement. The va1ves have been designed to regu1ate the downstream

pres-2

sure in the pressure range between 1.05 and 5 kg/cm for rates of flow vary-ing between 0.016 to 2.750 kg/sec (MKS).

The time to pump up the reservoir from atmospheric pressure is 3 1/2 hours.

AIRCRAFT MODELS WITH POWERED PROPELLERS

Sma11 motors which can be fitted in mode1s to drive propellers are inc1uded in the tunnel equipment. Power supply to these motors is through a variab1e frequency set consisting of a d.c. generating set driving a d.c. motor coupled to a 220 V 12 KW 500 C/sec. Alternator motors avai1ab1e for

propellers are of 3 types :

1) 220 V, 15.000 RPM, 2 H.P. 2} 220 V, 30.000 RPM, 1 H.P.

3) 24 V, 30.000 RPM, 3 H.P. with a 220/24 V transformer.

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TUNNEL MOTOR

SPEED OONTROL POTENTIOMETER

MAIN

D.C GENERATOR

AUXILIARY MOTOR-GENERATOR SETS

SCHEMATIC LAYOUT OF ELECTRICAL CIRCUITS

. FIG.3 8.000 V IV SYNCHRONOUS MOTOR 220V tv

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COLLECTOR ABOVE WORKING SECTION L -OF SPI N TUNNEL.

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41 WIRE COIL.

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FUSES O.C. SUPPLY. d.e. MOTOR 220V. ~

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BALANCE

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LOWER PLATE

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FIG.7A. SIX COM PONENT BALANCE WITH MODE L SUSPEN DEO BE LOW 1 N OPEN JET TEST SEC TION

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10 m3

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PRESSURE AIR SUPPLV.

ORIFICE PLATE

FOR RATE OF FLOW M EASUREM ENT.

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4 M A TIC TpRESSURE

REGULATING VALVES.

2 STAGE 10 H.P. COMPRESSOR

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,STOP VALVE 'STOP VALVE

hUXILIARY RESERVOIR

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TCEA TM 8

Training Center for Experimental

A erodypami cs •

LA SOUFFLERIE A FAIBLE VITESSE L-1

DU C.F.A.E.

Oct. 1960 pau1.Colin

Une description de la soufflerie à

faible vitesse L-l du C.F.A.E. est don

née. De conception particulière, cette

soufflerie peut être utilisée soit en veine libre de 3 m de dia., soit en veine guidée de 2 m de dia., soit enfin

en veine verticale (soufflerie de vril-'

le) de 3 m de dia.

1. COLIN, Paul

Il. TCEA TM 8

TCEA TM 8

Aerodynamics.

LA SOUFFLERIE A FAIBLE VITESSE L-l DU C.F.A.E.

Oct. 1960 Paul Colin

faible vitesse L-l du C.F.A.E. est

don-née. De conception particulière, cettE

soufflerie peut être utilisée soit en

I

I.

veine libre de 3 m de dia., soit en 11.

veine guidée de 2 m de dia., soit enfi~

en veine verticale (soufflerie de vril

Ie) de j m de dia.

COLIN, Pau1

TCEA TM 8

TeEA TM 8

A erodynami cs.

THE T.C.E.A. LOW SPEED TUNNEL L-l

Oct. 1960 Paul.Colin

A description of the TCEA low speed

tunnel L-l is given. Of unusual

de-sign, this tunnel can be operated in three different configurations namely as an open jet tunnel of 9.8 feet dia., as a closed working section tunnel of

6.5 feet dia. or as a vertical jet

(spin) tunnel of 9.8 feet dia.

TCEA TM 8

Aerodynamics.

de-sign, this tunnel can be operated in

I. COLIN, Paul Il. TCEA TM 8

three different configurations namely

:1

I. COLIN, Pau1

as an open jet tunnel of 9.8 feet dia.,~I. TCEA TM 8 as a closed working section tunnel of

6.5 feet dia. or as a vertica1 jet (spin) tunnel of 9.8 feet dia.

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TCEA TM 8

Aerodyp.amics.

LA SOUFFLERIE A FAIBLE VITESSE L-l

DU C.F.A.E.

Oct. 1960 Paul,Co1in

née. De conception particulière, cette

soufflerie peut être uti1isée soit en veine libre de 3 m de dia., soit en veine guidée de 2 m de dia., soit enfin

en veine verticale (soufflerie de

vril-le) de 3 m de dia.

1. COL IN , Paul

Il. TCEA TM 8

TCEA TM 8

Aerodynamics.

LA SOUFFLERIE A FAIBLE VITESSE L-l

DU C.F.A.E.

Oct. 1960 Pau1 Colin

née. De conception particulière, cettE

soufflerie peut être utilisée soit en

I

I.

veine libre de 3 m de dia., soit en 11.

veine guidée de 2 m de dia., soit enfin

en veine verticale (soufflerie de vril~

Ie) de 3 m de dia.

COLIN, paul

TCEA TM 8

Aerodynamics.

Oct. 1960 Paul.Colin

de-sign, this tunnel can be operated in three different configurations namely as an open jet tunnel of 9.8 feet dia., as a closed working section tunnel of 6.5 feet dia. or as a vertical jet

(spin) tunnel of 9.8 feet dia.

TCEA TM 8

Aerodynamics.

THE T.C.E.A. Lav SPEED TUNNEL L-l

de-sign, this tunnel can be operated in

1. COLIN, paul

Il. TCEA TH 8

three different configurations namely

:1

I. COLIN, paul

as an open jet tunnel of 9.8 feet dia.,~I. TCEA TM 8

as a closed working section tunnel of

6.5 feet dia. or as a vertical jet